It has been claimed that a great deal of AI research is an attempt to discover the empirical laws describing a new type of entity in the world—the artificial computing system. I call this enterprise 'medium AI', since it is in some respects stronger than Searle's 'weak AI', and in other respects weaker than 'strong AI'. Bruce Buchanan, among others, conceives of medium AI as an empirical science entirely on a par with psychology or chemistry. I argue that medium AI is not an empirical science at all. Depending on how artificial computing systems are categorized, it is either an a priori science like mathematics, or a branch of engineering